Sanitary napkins and disposable diapers have been conventionally used as absorbent articles. And pee pads for pets included within the category of the above absorbent articles are also widely used as toilets for pets. A liquid permeable top sheet is provided to the part of such absorbent articles which contacts such as the user's skin. And recently, bulky nonwoven fabric is preferred as the material of the top sheet since a high capturing performance is required from the viewpoint of reducing the sticky touch felt by the skin.
Such nonwoven fabric is manufactured in a strip form by appropriate methods such as the carding method, and are wound in a rolled form thereafter to be stored in states of nonwoven fabric rolls. And the nonwoven fabric roll is brought to the absorbent article manufacturing line when the nonwoven fabric is to be used, then the nonwoven fabric is unrolled from the above nonwoven fabric roll at the above manufacturing line to be used as the material for the top sheet.
Meanwhile, tensile force in the winding direction is applied in order to avoid the nonwoven fabric from meandering and the like when winding the nonwoven fabric into a roll of nonwoven fabric. For such reason, the nonwoven fabric is usually wound tightly by this tensile force. In other words, this nonwoven fabric is compressed in the thickness direction to be in a state such that the bulkiness is reduced. Therefore, only nonwoven fabric with its bulk reduced would be unrolled and provided when the nonwoven fabric is unrolled from the nonwoven fabric roll at the absorbent article manufacturing line, that is, the aforementioned requirement of a bulky nonwoven fabric would not be met.
There is known, as a method of increasing the bulk of nonwoven fabric, a process such as blowing hot air against the surface of the nonwoven fabric to heat the surface of the nonwoven fabric so that the fibers of the compressed nonwoven fabric would return to its initial state. PTL 1 discloses, for example, a method of preparing a heating chamber for heating nonwoven fabric and blowing hot air into either the entrance side or the exit side when the nonwoven fabric is transferred from the entrance side to the exit side of the heating chamber. The hot air blown into the heating chamber is discharged from the other side of the entrance or the exit so to flow along the surface of the nonwoven fabric in the heating room allowing the nonwoven fabric to recover its bulk.